C# Console 學習筆記

#C# Console 學習筆記 | 来源: 网络整理| 查看: 265

綜合存取 App.config Key資料庫存取IO 資料讀入Struct存取 Local JSON File大數運算物件導向物件的建構建構子的繼承 / 呼叫父類別的建構子 Constructor Inheritanceis / as OperatorVirtual / Override / SealedOut 參數修飾Readonly 修飾詞Null 條件運算子 (C#6)封裝 Field 與讀取 Property 的範例取得執行中物件的型別 (typeof / GetType)字串處理集合類型集合類型的初始建構 Collection initializers匿名類型建構 Anonymous Types匿名類型的集合建構 List of Anonymous Types索引子範例 Examples of Indexer字典示範 (Examples of Dictionary)

C# is good to use and good to learn.

綜合存取 App.config Key

步驟1：加入參考：System.Configuration

步驟2：設定 App.config

步驟3：程式引用 config 值

using System.Configuration; static void Main(string[] args) { Console.WriteLine(ConfigurationManager.AppSettings["configKey"]); } 資料庫存取

⚡如果要 Insert String 包含中文等文字，必須要在 quote mark 之前加入N。

Insert Into tbName Values(N'櫻花', N'さくら');

🦄 否則必須使用 SqlCommand.Parameters

SqlCommand cmd = new SqlCommand(); cmd.CommandText = "insert into tbName (item) values (@flower)"; cmd.Parameters.Add("@flower", SqlDbType.NVarChar).Value = "さくら";

資料庫存取的範例

using System.Data.SqlClient; static void Main(string[] args) { string Constr = "Persist Security Info=False; Integrated Security=true; \ Initial Catalog=...;Server=...;"; SqlConnection dataConnection = new SqlConnection { ConnectionString = Constr }; dataConnection.Open(); SqlCommand mySqlCmd = new SqlCommand("Insert into ...", dataConnection); mySqlCmd.ExecuteNonQuery(); dataConnection.Close(); } IO 資料讀入string text = System.IO.File.ReadAllText(@"C:\filePath\file.txt", System.Text.Encoding.Default); Struct

struct屬於value type，因此在複製時是直接複製一份而非複製參考。而value type不可以被指為null，反之，reference type則可以。除非是nullable value type。

public struct Point { public int X, Y; } static void Main() { Point p1 = new Point(); p1.X = 7; Point p2 = p1; // Assignment causes copy Console.WriteLine (p1.X); // 7 Console.WriteLine (p2.X); // 7 p1.X = 9; // Change p1.X Console.WriteLine (p1.X); // 9 Console.WriteLine (p2.X); // 7 } 存取 Local JSON Fileusing System.IO; using Newtonsoft.Json; public static List readJson() { var r = new List{}; using (var sr = new StreamReader( System.Web.HttpContext.Current.Server.MapPath("~/App_Data/member.json"))) { r = JsonConvert.DeserializeObject(sr.ReadToEnd()); } return r; } 大數運算using System.Numerics; BigInteger bigIntFromInt64 = new BigInteger(12345678901234567890); Console.WriteLine(bigIntFromInt64); string positiveString = "123456789012345678901234567890"; BigInteger posBigInt = BigInteger.Parse(positiveString); Console.WriteLine(posBigInt);

😋

物件導向物件的建構

避免濫用 Constructor Overloadding ，如果只是不同 Fileds 的建構情境用 Object Initializer 替代，Object Initializer 是使用不含引數格式的建構子來進行，如果當此建構子不能被存取，使用 Object Initializer 就會發生錯誤。

public class Point{ public int X {get; set;} public int Y {get; set;} } new Point{ X = 5, Y = 15};

MSDN - How to initialize objects by using an object initializer

建構子的繼承 / 呼叫父類別的建構子 Constructor Inheritancepublic class Subclass : Baseclass { public Subclass (int x) : base (x) { } } is / as Operator is : 判斷變數是否指向特定型別(明確指定) as : 將型別轉型，若轉型失敗會指向null而非拋出錯誤 Virtual / Override / Sealed

class 方法有被 virtual 修飾的可以被繼承的 sub class override，如果沒有特別指定 virtual 與 override 則 sub class 會隱藏 pareant method。若方法被 sealed override，則不能再被繼承者 override。

Out 參數修飾

讓引數變成 Reference Value，可以讓函數外的變數接收函數內的值；在使用 TryParse 時會用到。

int initializeInMethod; OutArgExample(out initializeInMethod); Console.WriteLine(initializeInMethod); // value is now 44 void OutArgExample(out int number) { number = 44; } string numberAsString = "1640"; int number; if (Int32.TryParse(numberAsString, out number)) Console.WriteLine($"Converted '{numberAsString}' to {number}"); else Console.WriteLine($"Unable to convert '{numberAsString}'"); // The example displays the following output: // Converted '1640' to 1640

MDSN - Out

Readonly 修飾詞

可以保證 Field 只被初始化一次，並且不會重複初始化以免讓資料流失。

public class Customer { public readonly List Orders = new List(); //物件建構時，自動初始化 } Null 條件運算子 (C#6)

C# Null Conditional Operator, Null 條件運算子

封裝 Field 與讀取 Property 的範例public class Person { public DateTime BirthDate {get; set;} public int Age { get { var timespan = DateTime.Now - BirthDate; return timespan.Days / 365; } } } 取得執行中物件的型別 (typeof / GetType)p.GetType().Name typeof (Point).Name 字串處理

C# String 字串處理

集合類型集合類型的初始建構 Collection initializersList digits = new List { 0, 6, 1, 9 }; List fruits = new List { "Mango", "Lichee", "Lemon" }; List points = new List { new Point{X = 3, Y = 5}, new Point{X = 2, Y = 7} }; var dict = new Dictionary() { { 017, new StudentName { Name = "sdwh", ID = 5017 } }, { 028, new StudentName { Name = "phym", ID = 5028 } }, { 099, new StudentName { Name = "mike", ID = 5099 } } };

MSDN - Object and Collection Initializers (C# Programming Guide)

匿名類型建構 Anonymous Typesvar pet = new { Age = 10, Name = "Fluffy" };

MSDN - Anonymous Types

匿名類型的集合建構 List of Anonymous Typesvar anonArray = new[] { new { name = "apple", number = 4 }, new { name = "grape", number = 1 }, }; foreach (var fruit in anonArray) { Console.WriteLine($"{fruit.name} {fruit.number}"); } 索引子範例 Examples of Indexer

範例 1

public class HttpCookie { private readonly Dictionary _dictionary; public DateTime Expire {get; set;} public HttpCookie() { _dictionary = new Dictionary(); } public string this[string key] { get { return _dictionary[key];} set { _dictionary[key] = value;} } }

範例 2

class Sentence { string[] words = "The quick brown fox".Split(); public string this [int wordNum] // indexer { get { return words [wordNum]; } set { words [wordNum] = value; } } } static void Main() { Sentence s = new Sentence(); Console.WriteLine (s[3]); // fox s[3] = "kangaroo"; Console.WriteLine (s[3]); // kangaroo } 字典示範 (Examples of Dictionary)var d = new Dictionary(); d.Add("One", 1); d["Two"] = 2; // adds to dictionary because "two" not already present d["Two"] = 22; // updates dictionary because "two" is now present d["Three"] = 3; Console.WriteLine (d["Two"]); // Prints "22" Console.WriteLine (d.ContainsKey ("One")); // true (fast operation) Console.WriteLine (d.ContainsValue (3)); // true (slow operation) int val = 0; if (!d.TryGetValue ("onE", out val)) Console.WriteLine ("No val"); // "No val" (case sensitive) // Three different ways to enumerate the dictionary: foreach (KeyValuePair kv in d) // One ; 1 Console.WriteLine (kv.Key + "; " + kv.Value); // Two ; 22 // Three ; 3 foreach (string s in d.Keys) Console.Write (s); // OneTwoThree Console.WriteLine(); foreach (int i in d.Values) Console.Write (i); // 1223 Console.WriteLine();

【本文地址】

公司简介

联系我们